The hygiene hypothesis has its complexities and
contradictions, but the basic idea is this: If the
Liflanders had wanted to prevent Cameron's allergies,
they should have moved a cow into their living room.
Good dirt His mother calls him Dominik, but to scientists in Bavaria,
Germany, he is G-00195-one of 1,163 children participating in
a five-nation study to see why farm children tend to be less prone
to allergies. The study's director, Erika von Mutius, at Children's Hos
pital at the University of Munich, thinks early exposure to beneficial
microbes in dirt and animal waste may help the immune system
distinguish later in life between real threats and bogus ones.
122 NATIONAL GEOGRAPHIC * MAY 2006